The cyanobacterium, Nostoc punctiforme can protect against programmed cell death and induce defence genes in Arabidopsis thaliana.

Many cyanobacteria can form nitrogen-fixing symbioses with a broad range of plant species. Unlike other plant-bacteria symbioses, little is understood about the immunological responses induced by plant cyanobionts (symbiotic cyanobacteria). Here, we used Arabidopsis thaliana suspension cell cultures as a model system to demonstrate that the model plant-symbiotic cyanobacteria, Nostoc punctiforme is capable of protecting against plant programmed cell death (PCD). We also profiled the early transcriptomic changes that were induced in response to conditioned medium (CM) from N. punctiforme cell cultures. Interestingly, the PCD reduction was preceded by the induction of genes associated with defence and immunity, the most striking of which were a number of WRKY-family transcription factors. Down-regulated included genes involved in the regulation of cell growth and differentiation. This work is the first to show that a cyanobacteria can regulate plant PCD and provides a useful transcriptome resource for studying early plant cell responses to symbiotic cyanobacteria. Overall design: Arabidopsis thaliana suspension cell cultures were incubated with a 20% volume/volume of conditioned medium (CM) from Nostoc punctiforme liquid cultures. As a control treatment, cells were instead incubated with a 20% volume of fresh N. punctiforme growth medium (BG) (growth medium in which no cells were previously grown). After incubation for 1 hour, A. thaliana cells were harvested and RNA extracted for transcriptomic profiling.